Mechanically retained wear-resistant ceramic pad

ABSTRACT

A ceramic-metal composite structure which minimizes tensile ceramic loads and accommodates differences in thermal expansion characteristics between a metal member and a ceramic member without reliance on precise feature control for either member. The composite includes a mechanical retainer which allows a loose fitting relationship between the metal and ceramic members. The ceramic member is secured within a receiving bore in the metal member by the retainer in a manner which eliminates the need for precise machining of the ceramic and metal members. The metal member may be configured to accept either an internal or an external mechanical retainer element. The composite ceramic-metal structure of the present invention finds particular utility in forming a durable wear-resistant interface in internal combustion engine actuator or actuating components, such as compression brake master pistons.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates generally to wear-resistant ceramic-metalcomposite structures. More particularly, this invention relates to aninternal combustion engine component formed from a ceramic elementmechanically retained within a metal element.

Description of Related Art

The harsh operating conditions encountered in an internal combustionengine, particularly the high temperatures and high pressures, causeengine components to wear rapidly. Mechanically driven actuators andactuating components are especially susceptible to wear in thisenvironment. Consequently, the materials used for producing actuatingengine components should provide good mechanical strength, thermalstability and wear resistance. Metals have typically been used to formsuch components. However, ceramics, such as zirconia, silicon nitride,silicon carbide and the like, have been found to exhibit excellentmechanical strength, thermal stability and wear resistance. As a result,ceramics are increasingly being used as structural materials forcomponents of gas turbine engines and diesel engines.

Ceramics, despite their promise as wear-resistant engine components, aregenerally hard and brittle and lack the formability and workability ofmetals which are conventionally applied to low cost precision enginecomponents. Composites formed from a ceramic element and a metal elementhave been proposed to overcome these limitations. Although ceramic andmetallic composite structures useful as internal combustion enginecomponents are available, a ceramic-metal composite structuresufficiently reliable and durable for use as an actuating component inan internal combustion engine environment has not heretofore beencommercialized. The low thermal expansion and tensile strengthproperties of structural ceramics relative to metals in general make theformation of the secure connection between these two elements requiredin an actuating component difficult to achieve. It is presentlynecessary to machine each element to produce tolerances that are notonly sufficiently precise to ensure the retention of the ceramic elementin the metal element during engine operation, but which also allow forthe differential thermal expansion of the ceramic and the metal, andlimit tensile stresses in the ceramic.

A number of methods for securing a ceramic element to a metallic elementhave been developed which attempt to reduce the possibility of bondfailure due to differences in the thermal coefficient of expansionbetween the ceramic and the metal. U.S. Pat. No. 3,820,523, to Showalteret al, U.S. Pat. No. 4,508,067 to Fuhrmann, U.S. Pat. No. 4,643,144 toFingerle et al, and U.K. Patent Application No. 2 127 928A, for example,all disclose the bonding of a ceramic element to a metal element to formcomposite structures useful as engine components The compositesdisclosed in these patents employ an epoxy, an elastomer or some type ofadhesive to fix the ceramic element to the metal element.

U.S. Pat. No. 4,643,144 also discloses providing a ceramic insert to befitted into a metal element with geometrically shaped elevations anddepressions on one side to accommodate areas of greater and lesserthickness in an elastomeric bonding layer to compensate for expansiondifferences in the metal and ceramic. The ceramic-metal compositedisclosed in this patent still requires close tolerance machining ofboth the ceramic insert and the metal component to bond these elementssecurely together. Such precision machining is time-consuming and canincrease significantly the cost of an internal combustion enginecomponent that must be produced in this manner.

It is also known to secure a ceramic component to a metal component byan interference fit between the two components to form a compositestructure useful in an internal combustion engine. U.S. Pat. No.4,366,785 to Goloff et al, for example, discloses a tappet for aninternal combustion engine with a ceramic wear resistant insertmaintained within the annular metal rim of the main body of the tappetby an interference fit. The wear resistant insert is formed to beslightly larger in diameter than the diameter of the recess into whichit is fitted. The ceramic insert is forced into the recess undersufficient pressure to press fit it in the tappet main body. The insertis not required to be sized to fit exactly within the recess in thetappet, but must be slightly larger than the recess. However, to providea secure interference fit without damaging the metal or ceramiccomponents, each must still be formed to close tolerances.

Additional examples of metal-ceramic composite bodies joined usinginterference fit methods are disclosed in U.S. Pat. No. 4,614,453 toTsuno et al, U.S. Pat. No. 4,794,894 to Gill, assigned to Cummins EngineCompany, Inc., assignee of the present invention, and U.S. Pat. No.4,806,040 to Gill et al, also assigned to Cummins Engine Company, Inc.

U.S. Pat. Nos. 4,667,627 and 4,709,621 to Matsui et al disclose engineparts which include ceramic elements or inserts which are attached tometallic elements. Specifically, the ceramic inserts may be attached byshrink-fitting or press fitting. The ceramic may also be joined to themetal with a metallized layer of metal paste formed from a metal powderselected according to the composition of the metal used for the metalcomponent part. Each of these methods still requires that the metalcomponent and the ceramic insert be machined to specific tolerances,however.

Another method of securing a ceramic wear resistant element to a metalelement utilizes a separate connecting element or retaining element.U.S. Pat. No. 4,325,647 to Maier et al discloses a connecting elementfor ceramic and metallic parts formed from an insulating resilient bodyof a ceramic material. The thermally or mechanically induced differencesbetween the ceramic and metal structures are equalized, and contactstress in the operating state is limited. The insulating body positivelyconnects the ceramic and metallic elements and operates effectively tosecure these elements when it has specific physical characteristics, forexample, a thermal conductivity of 0.02 to 0.25 W/cmK at a temperaturedifference between the ceramic and the metallic structural elements ofabout 100° to 1500° C. and an elastic modulus of about 5000 and 150,000N/mm². This composite, however, is not intended to be used in theinterface between a mechanically driven actuator or actuating component,but in connection with a piston in the engine cylinder.

External connectors have been proposed for joining a ceramic element toa metal element. For example, U.S. Pat. No. 4,883,911 to Haahteladiscloses a ceramic piston ring carrier held in place on a metal pistonby casting in or with a locking ring to improve force transmission andfrictional conditions between the piston and the cylinder. U.S. Pat. No.4,848,286 to Bentz, assigned to Cummins Engine Co., also discloses theuse of an external metal connector for joining ceramic and metalcomponents of a pivot rod. Neither of these patents, however, suggeststhat the arrangement described therein could be used to secure a ceramicelement to a metal element to form a wear-resistant interface betweenengine actuator and actuating components.

Metal and ceramic elements may be connected by integrally shaping eachelement to produce a secure bond between the ceramic and metal elements.For example, U.S. Pat. No. 4,404,935 to Kraft discloses a ceramic cappedpiston wherein the ceramic piston cap is fitted into a recess and joinedto a metal piston by intermeshing radial flanges biased into engagementwith the piston by a spring. Both the ceramic cap, which is intended toprovide heat insulation rather than wear resistance, and the metalpiston require special machining or casting to provide the necessaryintermeshing radial flanges.

The prior art, therefore, has failed to provide a ceramic-metalcomposite structure in which a ceramic element is reliably and durablyretained by a metal element so that the composite can be used to form awear-resistant interface between actuating and actuator components in ainternal combustion engine. The prior art has further failed to providea ceramic-metal composite that is sufficiently reliable to be useful asa driven actuator or actuating component in an internal combustionengine that can be produced inexpensively in high volume on a largescale so that the production of such components is commerciallyfeasible.

SUMMARY OF THE INVENTION

Therefore, it is a primary object of the present invention to overcomethe deficiencies of the prior art and to provide a reliable commerciallyuseful wear-resistant metal and ceramic composite capable ofwithstanding stresses produced in the interface between a mechanicallydriven actuator and an actuating component.

It is another object of the present invention to provide a ceramic-metalcomposite structure wherein a ceramic element is joined securely to ametal element without reliance on close tolerance feature control foreither element.

Yet another object of the present invention is to provide aceramic-metal composite structure geometrically configured to minimizetensile ceramic loads and accommodate the differences in the thermalexpansion behavior of the ceramic.

Still another object of the present invention is to provide a durableand reliable ceramic-metal composite structure wherein a ceramic elementis mechanically retained within a metal element.

Yet a further object of the present invention is to provide aceramic-metal composite structure useful for forming a wear-resistantactuating or actuator component of an internal combustion engine whereina ceramic element is retained in a metal element by a mechanicalretainer interior to the composite structure.

A still further object of the present invention is to provide aceramic-metal composite structure useful for forming a wear-resistantactuating or actuator component of an internal combustion engine whereina ceramic element is secured to a metal element by a mechanical retainerexterior to the composite structure.

The foregoing objects are achieved by providing a ceramic-metalcomposite structure which minimizes tensile ceramic loads, accommodatesdifferences in thermal expansion behavior, and which secures these twoelements without reliance on precise feature control. The ceramic-metalcomposite of the present invention produces commercially useful,reliable and durable wear-resistant internal combustion engine actuatingor actuator components. The ceramic element is received in a recess inthe metal element, where it is held securely by either internal orexternal mechanical retaining means. The configuration of the ceramicelement and the metal element recess are selected according to the typeof retaining means used to provide a secure connection between theceramic element and the metal element without the precision machiningrequired by the prior art. The ceramic-metal composite structure of thepresent invention is especially capable of withstanding the stressesproduced in the interface between a mechanically-driven actuator and anactuating component in an internal combustion engine, such as thoseencountered in a compression brake master piston.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut-away, cross-sectional side view of oneembodiment of a compression brake incorporating the ceramic-metalcomposite structure of the present invention;

FIG. 2 is a top view of an internal mechanical retaining element of thepresent invention;

FIG. 3 is a partially cut-away, exploded cross-sectional side view ofthe master piston of FIG. 1 prior to assembly which includes across-sectional view of the retaining element taken along line 3--3 ofFIG. 2;

FIG. 4 is a partially cut-away, cross-sectional side view of a secondembodiment of the present invention;

FIG. 5 is a partially cut-away, cross-sectional side view of a thirdembodiment of the present invention;

FIG. 6 is a partially cut-away, cross-sectional side view of a fourthembodiment of the present invention;

FIG. 7 is a partially cut-away, cross-sectional side view of a fifthembodiment of the present invention prior to assembly;

FIG. 8 is a partially cut-away, cross-sectional side view of the fifthembodiment illustrated in FIG. 7 after assembly;

FIG. 9 is a partially cut-away, exploded cross-sectional side view of asixth embodiment of a compression brake master piston designed inaccordance with the present invention prior to assembly;

FIG. 10 is partially cut-away, cross-sectional side view of the pistonillustrated in FIG. 9 after assembly;

FIG. 11 is a partially cut-away, cross-sectional side view of a seventhembodiment of the present invention;

FIG. 12 is a partially cut-away, exploded cross-sectional side view ofan eighth embodiment of the present invention prior to assembly;

FIG. 13 is a partially cut-away, exploded cross-sectional side view of avariation of the FIG. 12 embodiment of the present invention prior toassembly;

FIG. 14 is a partially cut-away, exploded cross-sectional side view of asecond variation of the FIG. 12 embodiment of the present inventionprior to assembly;

FIG. 15 is a partially cut-away, cross-sectional side view of acompression brake master piston assembly designed in accordance with thepresent invention; and

FIG. 16 illustrates the master piston assembly of FIG. 15 in operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a wear-resistant ceramic and metalcomposite structure which combines the machinability of metal with thethermal and mechanical wear resistance of ceramic that is especiallywell-suited for forming driven actuator or actuating internal combustionengine components. Prior combinations of metal and ceramic members forturbine and diesel engine components have required close tolerancesbetween each of the members to prevent any separation of the membersand, as a result, have been expensive to produce. These composites havenot always been as reliable as might be desired. The present inventionovercomes the shortcomings of prior art ceramic-metal compositestructures by providing a simple mechanical structure that allows aceramic element to be reliable and durably retained within a metalelement to form a ceramic-metal composite which can be easily andinexpensively formed. Reliable ceramic-metal engine actuating oractuator components can now be readily produced in commercially usefulquantities. The mechanical retaining element of the present inventioneffectively secures a wear-resistant ceramic member within a metalengine component to form a durable, wear-resistant interface betweensuch mechanically actuated engine components as hydraulic tappet slidingcam followers and compression brake master pistons. Moreover, the enginecomponents produced according to the present invention do not requirecostly precise machining.

Referring to the drawings, FIG. 1 illustrates a compression brake masterpiston 10. Although this and the remaining Figures discuss the presentinvention in a compression brake master piston environment, the presentinvention may also be used to form a wear-resistant metal and ceramiccomposite which is capable of withstanding stresses produced at anyinterface between a mechanically driven actuator and an actuatingcomponent, such as, for example, a tappet sliding cam follower or acrosshead pad. Piston 10 is made from a metal element 11, which ispreferably made of steel, and a ceramic element or pad 12 located withina central receiving recess or bore 14 in the metal element. The presentinvention contemplates the use of a wide variety of ceramics, such as,for example, zirconia, alumina, zirconium alumina composites, andsilicon nitride to form the ceramic element 12. Generally, the ceramicelement or pad 12 is shaped such that a first fitted portion 16 of thepad fits within bore 14 and a second contact portion 18 of the padextends therefrom to provide a wear-resistant interface 19 on theactuating member, piston 10.

A retainer element 20 engages a shoulder or flange 22 located betweenthe first portion 16 and the second portion 18 of pad 12 when it ispositioned in place within the piston bore 14. The flange 22 permits pad12 to rest easily on retainer 20 of first and second portions 16 and 18.A fillet 23 is formed at the transition between the two differentdiameters to facilitate pad molding and to reduce the stressconcentrating effect of the corner that would otherwise be producedwhere the first and second portions are joined. Retainer 20 isillustrated to have a ring shape in FIGS. 1-2; however, as will becomeapparent with references to FIGS. 4-8, the retainer element 20 may beconstructed to have a variety of ring-type configurations.

FIG. 2 illustrates one embodiment of retainer element 20 in top view. Asillustrated therein, retainer 20 is a ring having a cut or split 24 toallow the ring to press fit into bore 14. The ring may be a square wireas shown composed of a resilient spring steel to ensure that onlyelastic deformation occurs upon insertion of the ring into bore 14.After insertion, the split ring returns or springs back to its originaldimensions to maintain a secure position within the bore. However, theretainer element 20 could have other configurations and could be formedof other materials which will achieve this same purpose.

FIG. 3 provides a more detailed view of each of the components prior toassembly. Receiving bore 14 is formed by counter boring the metalelement 10 and forming a shallow groove 30 to receive the retainerelement 20. Therefore, the receiving bore 14 includes at least threedistinct sections, an interior small diameter section 26, and exteriorcircumferential ridge section 28 and the groove 30, which is a centrallarge diameter section. The diameter of interior section 26 is slightlylarger than the diameter of first portion 16 of pad 12. This permitsfirst portion 16 to be maintained within the receiving counterbore 14while second portion 18, having a sufficiently small diameter, extendsthrough retainer 20 to provide the wear-resistant interface betweenpiston 10 and a mechanically driven actuator (not shown). The centralsection 30 has a larger diameter than interior section 26 and exteriorsection 28 to provide a secure engagement location for the retainerelement 20. Further, an angular receiving face 32 is provided on theexterior side of exterior section 28 to facilitate the insertion ofretainer 20. The angular, sloped design of face 32 encourages thedeformation of retainer 20 during insertion. Once it clears exteriorsection 28, the retainer 20 may return to its original shape and fitsnugly within central groove 30. Preferably, counterbore 14 is drilledwithin piston 10 by a conventional drill or boring tool. The cone-shapedarea 34 represents a recess formed by the drill point when the drillingtool comes to rest within the bore 14 to complete the drilling process.

The structure of the ceramic element or pad 12 is also illustrated inFIG. 3 so that the fillet 23 between first portion 16 and second portion18 can be clearly seen. In addition, the preferred configuration of asection of the pad second portion 18 is shown in FIG. 3. The smallerdiameter contact face 19 assists in receiving the retainer element 20.

FIG. 4 illustrates a second embodiment of the present invention whereina layer of epoxy resin 36 is inserted between pad 12 and bore 14 toprovide a second or back-up means of retention when it is essential tofix the ceramic element within the metal element 11.

FIG. 5 illustrates a third embodiment of the present invention whereinthe retainer element is in the form of a disc 20a. The retainer disc 20ais designed to include a plurality of joints 38 having graduallyincreasing diameters. The outer diameter of disc 20a is sufficientlylarger than the inner diameter of central bore section 30, so that whendisc 20a is press fit into bore 14, the ends of the disc engage theexterior section 28. The inner diameter of disc 20a is similar to thatof the ring 20. The ceramic pad second portion 18 extends therethrough,and the pad 12 rests upon disc 20a at flange 22.

FIG. 6 illustrates a fourth embodiment of the present invention whichincludes a helical ring retainer 20b. Helical ring 20b, which has agenerally helical configuration, includes a split (not shown). Thehelical design permits a range of different sizes of ceramic pads 12 torest snugly against the upper extent of interior section 26, even whenthere are variations in the depth of bore 14. In addition, FIG. 6 showsan annular drill contact portion 34', demonstrating that differentdrilling tools can be used to provide the preferred bore configuration.

FIG. 7 illustrates a fifth embodiment of the present invention whereinthe retainer is a ring 20c formed of a soft metal caulking material.FIG. 7 shows ring 20c after its insertion into bore 14 but prior to theapplication of sufficient pressure to secure the ceramic and metalelements together. The soft metal ring 20c is pressed into the bore 14to plastically deform the ring into the central section 30 of the bore.The soft metal is preferably copper or aluminum. In this embodiment, theceramic pad is fixed within the bore 14. FIG. 8 illustrates piston 10after ring 20c has been pressed into the bore. Preferably, the height ofsecond portion 18 of pad 12 is such that about half of the secondportion is received within the bore 14. FIGS. 7 and 8 further illustratean additional embodiment of the ceramic pad 12. In this embodiment thesecond portion 18 of the pad has a constant diameter between the face 19and the shoulder 22.

FIGS. 9-11 illustrate another type of retainer element according to thepresent invention, an external cap 40 which engages the exterior of themetal member 11. The ceramic element or pad 12 is shaped as describedabove to include a first and second portion 16 and 18, respectively,with a fillet 23 therebetween. The second portion may have a constant oran increasing diameter. In this embodiment, however, the receiving bore14 does not include the shallow groove 30 as discussed above but,rather, is a simple counterbore having approximately the same dimensionsas the first portion 16 of pad 12. The metal member 11 is formed toinclude an external groove 42 and a circumferential ridge 44. Theexternal cap 40 actively engages the exterior of metal member 11 toretain ceramic pad 12 within the bore 14. To accomplish this, the cap 40includes a central opening 46 which has a diameter slightly larger thanthe diameter of second portion 18 of pad 12, but smaller than thediameter of first portion 16 to engage shoulder 22 as shown in FIG. 10.The ceramic pad is held securely in place and thus provides awear-resistant surface 19 for the actuating member or piston 10.

The external retaining cap 40 may include a variety of differentlyconfigured projections which assist in securing the ceramic element 12to the exterior of the metal element 11. For example, in FIGS. 9 and 10barbs 48 are spaced about the circumference of the cap 40. The barbs 48,which are sized in relation to the height of the circumferentialexternal groove 42 are bent toward the interior of the cap. When theceramic pad 12 is inserted into the bore 14 and the retainer cap 40 isin place, the barbs 48 will engage a ledge 43 formed between the groove42 and the circumferential ridge 44 as shown in FIG. 10. Any tendency ofthe ceramic element 12 to withdraw from the metal element will cause thebarbs 48 to engage the ledge 43 more securely.

FIG. 11 illustrates another embodiment of an external retainer element40a which can be used to hold a ceramic element 12 in a metal element11. The exterior surface of the metal element is formed to have an endsection 50 that has a slightly smaller diameter than the rest of themetal element, thus forming a shoulder 52. A peripheral groove 54 isformed in the end section 50. A corresponding circumferential tongue 56is formed on the interior surface of the retainer cap 40a so that whenthe retainer cap 40a is snapped over the end of the metal element 11 tohold the ceramic pad 12 in place, the tongue 56 fits in the groove 54 toassist in holding the cap 40a in place.

FIGS. 12, 13, and 14 illustrate, prior to and after assembly, anadditional embodiment and variations of this embodiment of the presentinvention whereby a ceramic element 12 may be held within a metalelement 11 to produce a secure composite with a wear-resistant face 19in an actuating or actuator component of an internal combustion engine.The retaining elements in each of these embodiments are heldsubstantially internally within bores in the metal elements and areconfigured to surround that portion of the ceramic element 12 that isactually received within the metal element 11. It will be noted thateach of the ceramic elements 12 in FIGS. 12-14 has a slightly differentconfiguration, particularly with respect to the height and diameter ofthe second portion 18. The height of the first portion 16 may also bevaried, depending in part upon the use of the ceramic-metal composite.

FIG. 12, for example, illustrates a ceramic element with first andsecond portions having approximately equal heights. The diameter of thefirst portion 16 is larger than the diameter of the second portion 18,and a fillet 23 is formed at the junction of these two portions as inthe FIGS. 1-11 embodiments. A narrowly chamfered portion 17 directlycontacts the interior of the metal element 11. In FIG. 13, the firstportion 16 is substantially greater in height than the second portion18, and the chamfered portion 17 is somewhat greater in height than thesecond portion. The FIG. 14 variation shows a large first portion 16 anda chamfered second portion 18 which is substantially equal in size tothe chamfered portion 17. In each instance the retaining elements 60a,60b and 60c include circumferential lips 61 which are received incorresponding recesses 62 in the bores 14 of each of the metal elementsshown in FIGS. 12-14. The FIGS. 12 and 13 variations include retainerelements 60a, 60b with circumferential ledges 64 to engage the shoulder22 of the ceramic elements. The FIG. 14 variation does not have a flangethat can be positively engaged by a ledge on the retaining element.Consequently, the retaining element 60c is shaped to correspond to thechamfer on second portion 18 of FIG. 14.

FIGS. 15 and 16 illustrate one application of the ceramic-metalcomposite of the present invention to form an actuating component inoperation in an internal combustion engine. In this application, theceramic-metal composite is the master piston 80 in a compression brake.Only a portion of the housing 82 is shown in FIGS. 15 and 16. When thebrake is in the "off" position shown in FIG. 15, the master piston 80 isheld in a retracted position substantially within the piston bore 84 inthe housing 82 by a leaf spring 86. The ceramic element or pad 88 isretained by the master piston 80 according to one of the internal orexternal retaining element structures discussed above. When the brake is"off" there is no contact between the piston and the rocker leveradjusting screw 90. The adjusting screw 90 is driven by the rocker leverin a combination of cyclic rotating and reciprocating motions asindicated by arrows a and b. Consequently, the hex head 92 of the screw90 both reciprocates as indicated by arrow b and rocks relative to thepiston 80. This causes a sliding while reciprocating interaction betweenthe screw and the piston during compression brake operation.

The master piston 80 and the head 92 of the screw 90 will contact eachother when the brake is in the "on" position shown in FIG. 16. In thisposition the piston is hydraulically extended from the bore 84 by fluidflowing into the bore at arrow c. When the hydraulic pressure on thepiston 80 exceeds the leaf spring retaining force, the piston is forcedinto contact with adjusting screw hex head 92. The piston 80 impacts theadjusting screw 90 once, and the piston is then driven by the screwuntil the brake is turned off. Continuous contact between the ceramicpad 88 and the screw head 92 is maintained at all times during braking.

The compression brake components are lubricated by splashing oil, thepreferred hydraulic fluid, and also by the leakage of high pressureactuation oil, between the piston 80 and the bore 84 in the brakehousing as shown by arrows d.

The piston 80 rotates freely about its longitudinal axis e within bore84 as shown by arrow f. This rotation beneficially distributes wear atthe piston--screw interfaces. Piston rotation may also beneficiallydistribute wear at the interface of the piston 80 and the piston bore84.

Brake operation time and brake operation cycles depend on manyvariables, including driving conditions, such as weather and highwaytopography, vehicle factors, such as power train performance and vehicleweight, and vehicle operator driving habits. For example, some operatorsuse the brake when shifting to higher gears (i.e. up shifting). Thebrake then remains in the "on" position shown in FIG. 16 to slow theengine between gear changes, which has the potential for producing wearat the interface between pad 88 and head 92. However, momentary brakedisengagement occurs automatically with each clutching sequence toprevent braking when the engine is disconnected from the transmission.

The typical axial piston load in the arrangement shown in FIGS. 15 and16 is about 1650 lbf, with a maximum axial load of about 2500 lbfencountered during transient conditions. Typical and maximum lateralpiston loads are about 200 lbf and 300 lbf, respectively. Theceramic-metal composite of the present invention has been found toprovide an economical, durable, wear-resistant interface for acompression brake master piston, even under a variety of adverseoperating conditions.

INDUSTRIAL APPLICABILITY

The ceramic-metal composite of the present invention will find itsprimary utility where economical, durable, wear-resistant interfacesbetween actuator and actuating components of internal combustion enginesare desired. While the mechanically retained ceramic-metal composite ofthe present invention is especially well-suited for forming the masterpiston in a compression brake, other engine actuating components mayalso be constructed as described herein.

We claim:
 1. A wear-resistant ceramic-metal composite structure capableof withstanding stresses produced at an interface between a mechanicallydriven actuator and an actuating component in an internal combustionengine, said composite structure comprising:(a) a ceramic element meanshaving a first fitted portion and a second contact portion wherein saidfirst portion is diametrically larger than said second portion to createa flange therebetween for forming said interface; (b) a metallic elementmeans including a stepped receiving bore located in an end thereof forreceiving said ceramic element means wherein the diameter of a firstinterior step in said receiving bore is smaller than the diameter of asecond step positioned exteriorly of said first step and said firstportion of said ceramic element means is fitted within said first step;and (c) retaining element means for retaining said ceramic element meansfirst portion within said receiving bore first interior step in saidmetallic element means so that said ceramic element means second portionextends exteriorly of said receiving bore second step to form saidinterface, wherein said retaining means engages said metallic member atsaid receiving bore second step and said flange of said ceramic elementmeans.
 2. The ceramic-metal composite structure of claim 1, wherein saidstepped receiving bore of said metallic element means includes aninterior small diameter section forming said first step, an exteriorcircumferential ridge section and a central large diameter groovesection forming said second step between the interior small diametersection and the exterior circumferential ridge section, wherein saidretaining element means is positioned within said central groovesection.
 3. The ceramic-metal composite structure of claim 2, whereinsaid exterior circumferential ridge section includes an inwardlydirected angular receiving face to facilitate the insertion of saidretaining element means.
 4. The ceramic-metal composite structure ofclaim 3, wherein said retaining element means is a ring which isdesigned to be press fit into said receiving bore and rest within saidcentral large diameter section.
 5. The ceramic-metal composite structureof claim 4, wherein said ring is a planar, circular structure having alarger internal diameter than the diameter of said second portion ofsaid ceramic element means to receive said second portion and engagesaid shoulder.
 6. The ceramic-metal composite structure of claim 4,wherein said ring comprises a soft metal which upon the application ofpressure plastically deforms into the circumferentially extendinginternal groove against said ceramic element means.
 7. The ceramic-metalcomposite structure of claim 6, wherein said soft metal is selected fromthe group consisting of copper and aluminum.
 8. A compression brakemaster piston of a compression brake assembly comprising:(a) a metallicmember located within a brake housing, said metallic member including atone end thereof a centrally disposed stepped receiving bore with acentral circumferentially extending internal groove; (b) awear-resistant ceramic member including a fitted portion diametricallylarger than a contact portion to create a shoulder therebetween, whereinsaid fitted portion fits within said metallic member stepped receivingbore and said contact portion contacts an adjusting screw of saidcompression brake assembly; and (c) a retaining means for retaining saidceramic member fitted portion within said stepped receiving bore of saidmetallic member where said retaining means engages said metallic membercircumferentially extending internal groove and said ceramic membershoulder.
 9. The compression brake master piston of claim 8, whereinsaid receiving bore further includes an inwardly directed angularreceiving face to facilitate the insertion of said retaining means. 10.The compression brake master piston of claim 9, wherein said retainingmeans is a ring which is designed to be press fitted into said receivingbore and rest within said circumferentially extending internal groove.11. The compression brake master piston of claim 10, wherein said ringis a planar, circular structure having a larger internal diameter thanthe diameter of said contact portion of said ceramic member to receivesaid contact portion and engage said shoulder.
 12. The compression brakemaster piston of claim 11, wherein said ring has an external diameterless than the diameter of said circumferentially extending internalgroove and includes a split to allow said ring to be press fit into saidreceiving bore and to resiliently expand within said groove.
 13. Thecompression brake master piston of claim 10, wherein said ring comprisesa soft metal which upon the application of pressure plastically deformsinto the circumferentially extending internal groove against saidceramic member.
 14. The compression brake master piston of claim 13,wherein said soft metal is selected from the group consisting of copperand aluminum.